This invention relates to a quick release mechanism for pivotally joined tube members and more particularly for use on foldable legs attached to supporting structures for signs, barriers, and the like.
There are many occasions when it is desirable to releasably attach a tube or the like to a structure. For example, a number of tubular legs are required to support a stand upon which an outdoor sign for conveying a message to passing motorists may be mounted. Frequently, the need is temporary, and it is therefore advantageous to have support stands for such signs which may be readily assembled and disassembled with very little effort on the part of the worker.
Often, such support stands comprise a base from which the mast to which the sign is attached extends upwardly. A plurality of legs, usually four, are pivotally attached to the base by means of bolts or similar fasteners, which extend through fastener holes in the legs and the stand base. The legs are each designed to pivot about the shank of their corresponding fastener from a folded, upright position for compact storage and easy transportability to an extended deployed position for supporting the sign. In both the folded and the extended positions each leg is fixedly attached to the base to prevent undesired pivoting. These attachments are removed when it is desired to pivot the legs from one position to the other, after which they are replaced.
Heretofore, such attachments have been accomplished using removable pins, bolts, clips, or by being manually tied upright. Most typically used presently are removable pin assemblies. In one such assembly, one pin is associated with each leg, usually by means of a chain or the like, so that it does not become lost. To fix the leg with respect to the stand in either the stowed or deployed position, the pin is manually inserted through a hole in the leg and engaged with a corresponding hole in the base plate of the stand. When it is desired to pivot the leg between the two positions, the pin is removed from the holes so that the leg is free to pivot about the pivotable connection between the leg and the stand base plate. Another pin assembly employs a spring biased pull pin for each leg, wherein the pin is attached to a coil spring within the tube leg. To lock the leg to the base plate of the stand, an opening in the leg is selectably aligned with one of the openings in the base plate of the stand, and the spring loaded pull pin is forced inwardly through the openings into the engaged position. The pull pin is unlocked by pulling it out of the opening.
Such attachment schemes, while effective, are relatively time consuming to operate, and involve a great deal of effort on the part of the Worker. In many cases a worker will have to bend over to release each of the four legs individually. This is potentially hazardous, since it diverts his concentration from the passing vehicular traffic. He also may have to remove his gloves to manipulate the pull pins.
U.S. Pat. No. 4,954,008 to Dicke et al discloses an alternative attachment arrangement which also utilizes a locking pin, as in the previously discussed arrangements, but further includes a leaf spring biased lever arm attached to the proximal end of the pin (that end which is closest to the worker). This handle permits the worker to depress the handle end of the lever arm to actuate the pin out of the hole in the stand base plate, thereby pivotally releasing the leg from the base plate. The bias of the leaf spring on the lever arm will return the pin to the engaged position as soon as the lever arm is released by the worker and the pin is aligned with a hole in the stand. This arrangement is an improvement over the previous methods, but still requires considerable effort on the part of the worker to engage the lever arm and depress it to release the leg. The worker must either bend over to squeeze it with his hand, or, with a fairly coordinated effort, push and depress the lever arm with his foot sufficiently to disengage the pin from the hole. Furthermore, it is necessary to repeat this effort four times in order to individually release all of the legs.
Another problem common to sign stands of the type described is the effect of repeated pivoting of the legs on the thin metal leg outer walls about the circumference of the fastener holes. Typically, the sign stands are roughly handled by the personnel responsible for setting them up and taking them down, with the legs being pivoted forcefully between the stowed and deployed positions. The applied force, combined with constant loading and unloading forces caused by wind and passing vehicles, causes the fastener shanks to contact the inner circumference of the fastener hole through the thin leg wall, causing rapid wear and elongation of the metal, until the fit of the shank within the elongated hole is so loose that the sign stand becomes wobbly. As this wear continues, the stand will eventually become unusable unless the leg with the elongated fastener hole is replaced. Replacing the legs is relatively expensive and inconvenient compared to the cost of replacing the entire sign stand, meaning that the wear of the leg fastener holes is usually the critical factor in determining the useful life of the stand.
What is needed, therefore, is a simple quick release mechanism which eliminates much of the repetitive effort on the part of the worker, and also requires simpler (and thus, safer), less complex motions than are required to actuate current leg release mechanisms. Additionally, some means for reducing wear of each leg fastener hole is necessary to increase the life span of the stand and thereby reduce expense.